As objects move through fluids, they are exposed to numerous forces that enhance or impede their progress. By analyzing and understanding these forces, one can predict the velocity of a moving object. Of the forces exerted on an object falling through a liquid, such as buoyant force or the force of gravity, the viscous or drag force appears to have the largest negative effect on the object. The effect of aero and hydrodynamic drag forces and friction appears underrepresented in high school physics courses.
Perhaps it is because concepts such as viscous and turbulent drag forces are difficult to predict and measure. My preliminary research indicated there are many factors affecting the forces on an object. These concepts fall in the field of fluid mechanics. Initially, my study began with the idea of measuring the aerodynamic drag force exerted on a model rocket. My primary interest was in the factors that influenced the maximum height reached by a rocket with a set amount of propellant.
I thought that launching a rocket on a particularly humid or hot day might result in a different maximum height than a launch on a colder day. It might be possible to theoretically identify the factors such as the pressure or density of the air, then relate them to the measured height. I soon realized that this experiment would not produce accurate data or a clear theoretical relationship because it involved a multitude of variables that were impossible to control without the use of a weather-controlling machine.
Progressing fromthis first idea, a more controllable experiment evolved: measuring and comparing the terminal velocities of a ball falling through glycerine at various temperatures. Glycerine was selected because its high viscosity1 exhibits demonstrable results. The amount of viscous drag within a given fluid appears to vary within a controlled container by temperature. This experiment was designed and conducted to test the following question: How is the terminal velocity of a ball falling through a column of glycerine affected by a change in the temperature of glycerine?
This study analysed the terminal velocities of an object falling under the force of gravity through a fluid at varying temperatures. My hypothesis states that as the temperature of the fluid decreases, the terminal velocity of the object will decrease by a proportion of. I base this prediction on the electrostatic bonding properties displayed in liquids. In order to prove this, an experiment will be conducted using a small metal ball and glycerine. The third force exerted on the ball, drag, is always in the opposite direction of the movement.
It is very similar to the friction force on a block sliding down a plane, which works in the opposite direction of the motion. The source of drag is derived from the viscosity of the fluid and the incidence of turbulence4 on the ball. At lower velocities, turbulence is small and laminar, whereas at higher velocities, turbulence becomes drastic and has an enormous effect on the drag force. One can use the Reynolds number, Re, a dimensionless value, to determine the nature of the flow (equation 4).